Pyridyl CO2 Fixation Enabled by a Secondary Hydrogen Bonding Coordination Sphere.

Reversible CO2 binders under ambient conditions are of significant interest for multiple applications in sensing and capture technologies. In this paper, a general systematic way to evaluate CO2 receptors with π-systems is put forward. A series of receptors (five pyridine-based and one triazine-based) are evaluated as CO2 binders in terms of number of hydrogen bonding sites, strength of hydrogen bond donors, and number of nucleophilic sites. The binding of CO2 to the receptors was probed by computational models, absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry, and 1H NMR studies. Multiple solvents with varying ionic strength additives are probed to analyze the effects on CO2-bound intermediates. The receptors were screened progressively down-selecting through the different analytical techniques arriving at a promising pyridine receptor, which shows evidence of CO2 binding with each of the analytical techniques. The diaminopyridine motif demonstrates reversible CO2 binding and has convenient substitution sites for derivatization to incorporate into functional sensor systems.

Water-Soluble NIR Absorbing and Emitting Indolizine Cyanine and Indolizine Squaraine Dyes for Biological Imaging.

Organic dyes that absorb and emit in the near-infrared (NIR) region are potentially noninvasive, high-resolution, and rapid biological imaging materials. Indolizine donor-based cyanine and squaraine dyes with water-solubilizing sulfonate groups were targeted in this study due to strong absorptions and emissions in the NIR region. As previously observed for nonwater-soluble derivatives, the indolizine group with water-solubilizing groups retains a substantial shift toward longer wavelengths for both absorption and emission with squaraines and cyanines relative to classically researched indoline donor analogues. Very high quantum yields (as much as 58%) have been observed with absorption and emission >700 nm in fetal bovine serum. Photostability studies, cell culture cytotoxicity, and cell uptake specificity profiles were all studied for these dyes, demonstrating exceptional biological imaging suitability.

Self-Assembling PCL-PAMAM Linear Dendritic Block Copolymers (LDBCs) for Bioimaging and Phototherapeutic Applications.

This study represents a successful approach toward employing polycaprolactone-polyamidoamine (PCL-PAMAM) linear dendritic block copolymer (LDBC) nanoparticles as small-molecule carriers in NIR imaging and photothermal therapy. A feasible and robust synthetic strategy was used to synthesize a library of amphiphilic LDBCs with well-controlled hydrophobic-to-hydrophilic weight ratios. Systems with a hydrophobic weight ratio higher than 70% formed nanoparticles in aqueous media, which show hydrodynamic diameters of 51.6 and 96.4 nm. These nanoparticles exhibited loading efficiencies up to 21% for a hydrophobic molecule and 64% for a hydrophilic molecule. Furthermore, successful cellular uptake was observed via trafficking into endosomal and lysosomal compartments with an encapsulated NIR theranostic agent (C3) without inducing cell death. A preliminary photothermal assessment resulted in cell death after treating the cells with encapsulated C3 and exposing them to NIR light. The results of this work confirm the potential of these polymeric materials as promising candidates in theranostic nanomedicine.

Donor-Acceptor-Donor NIR II Emissive Rhodindolizine Dye Synthesized by C-H Bond Functionalization.

A NIR II emissive dye was synthesized by the C-H bond functionalization of 1-methyl-2-phenylindolizine with 3,6-dibromoxanthene. The rhodindolizine (RhIndz) spirolactone product was nonfluorescent; however, upon opening of the lactone ring by the formation of the ethyl ester derivative, the fluorophore absorbs at 920 nm and emits at 1092 nm, which are both in the NIR II region. In addition, 4-cyanophenyl- (CNRhIndz) and 4-methoxyphenyl-substituted rhodindolizine (MeORhIndz) could also be prepared by the C-H activation reaction.

Counter Anion Effect on the Photophysical Properties of Emissive Indolizine-Cyanine Dyes in Solution and Solid State.

Near-infrared emissive materials with tunable Stokes shifts and solid-state emissions are needed for several active research areas and applications. To aid in addressing this need, a series of indolizine-cyanine compounds varying only the anions based on size, dipole, and hydrophilicity were prepared. The effect of the non-covalently bound anions on the absorption and emission properties of identical π-system indolizine-cyanine compounds were measured in solution and as thin films. Interestingly, the anion choice has a significant influence on the Stokes shift and molar absorptivities of the dyes in solution. In the solid-state, the anion choice was found to have an effect on the formation of aggregate states with higher energy absorptions than the parent monomer compound. The dyes were found to be emissive in the NIR region, with emissions peaking at near 900 nm for specific solvent and anion selections.